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Conference Article: Remarks on possibilities and limitations of theoretical approach to plate-out problems

Abstract

The knowledge of the interaction of the fission and activation products with primary circuit materials of HTR is of essential importance to normal operational conditions as well as to assessment of environmental risk connected with severe accidents. The HTR fuel development coated particles in graphite matrix assure several effective barriers against fission product migration. Nevertheless through these barriers or due to their damage a trace amount of the fission products reach the helium coolant. The most important of them from point of view of the plate-out phenomena are: Cs-137, Cs-134, Ag-110m, Ag-111, I-131, Sr-89 and Sr-90. Transported by helium coolant as free atoms molecules or adsorbed on graphite dust surfaces they can reach surface of primary circuit components. During the plate-out process at high temperature besides the adsorption and desorption important part start to play such phenomena as solubility and diffusion into bulk of the materials. Understanding of the processes involved in the transport from a gas to a surface phase and to a bulk solid is crucial to predict the plate-out results.

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Reference:

Specialists meeting on coolant chemistry, plate-out and decontamination in gas-cooled reactors Juelich, Federal Republic of Germany 2-4 December 1980

International Atomic Energy Agency, Vienna (Austria)

IWGGCR--2, pp:64-67